advanced open rotor noise prediction methods - spbstu.ru · advanced open rotor noise prediction...
TRANSCRIPT
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Advanced Open Rotor Workshop24th June 2008
Institute of Sound and Vibration ResearchUniversity of Southampton
Advanced open rotor noise prediction methods
Michael Kingan, ISVR
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
• Background– Advanced open rotor (AOR) architecture– Motivation for using AOR aircraft
• Available noise prediction methods– To predict sound pressure we need to know the flow over the rotor
blades– Computational– Analytic
• Analytic methods– Require induced flow to be expressed as a sum of various ‘sources’– Source descriptions
• Whole aircraft noise prediction– Installation (radiation and source) effects– Propagation effects
Presentation overview
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Advanced open rotor concept
• Two rows of counter-rotating propellers– Swirl off first blade row increases air velocity onto the second blade
row– Second blade row reduces swirl in wake– Much reduced weight and drag compared with a turbofan – Unsteady airflow onto the second blade row produces high levels of
noise• Promise significant reductions in fuel burn
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Background
• The AOR concept was considered during the 1980’s in response to high fuel prices at that time because of their good fuel efficiency.
• Development was not pursued for a variety of reasons, however chief among these was that oil prices fell
• Open rotor aircraft are being considered once more because of environmental and economic concerns however, noise is a prominent issue
• The noise spectrum produced by an AOR is expected to be dominated by tones, although there will be a significant broadband contribution
• Tone and broadband noise prediction models are being developed at the ISVR
• Prediction methods can be either analytic or numerical.
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Frequency
Soun
d Pr
essu
re L
evel
Broadband Noise
Tonal Components
Introduction to noise
• AOR’s produce both broadband noise and tones
• The human ear responds differently to tones and broadband noise• Typically noise with tonal contributions are more annoying than purely
broadband noise• Legislation usually penalises tonally dominated noise
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Tone Prediction Methods
• Two analytic methods have been identified – C. E. Whitfield, R. Mani, P. R. Gliebe (1990) High speed turboprop
aeroacoustic study, NASA CR 185242– A. B. Parry (1988) Theoretical prediction of counter-rotating propeller
noise, PhD Thesis• Computational schemes (numerous)
– Time consuming– Possibly more accurate
• Experimental validation – Extensive NASA report describing experimental validation of Whitfield
et al. code– Some good comparison presented in Parry
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Acoustic Radiation Formula
• AOR tones produced by interaction of flow produced by one blade row with the blades on the adjacent row
• An expression for the root-mean square acoustic pressure produced by each interaction tone is given by
• φs is a term due to the sweep of each blade• J is a Bessel function, whose argument is dependent on observer location
and thus greatly affects the ‘directivity’ of the tone (effectively a directional acoustic efficiency)
• S is a ‘source term’ which is effectively equal to the unsteady loading on the blade
• In order to calculate the acoustic pressure the unsteady loading terms must be determined for each source
( ) ( ) { }∫ −−
= ⎟⎠⎞
⎜⎝⎛
1sinexp
cos122 hzdzztRmkkJsizS
xMortBR
p θνφθπ
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Blade loading
• The unsteady blade loading is estimated using well-known ‘blade response functions’ which express the blade loading as a function of the upwash onto the propeller blades.
• Sears: used for gusts with ‘long’ (relative to the propeller chord) wavelengths
( )x
xcSkvrUp −−=Δ ωρ2Leading edge radiation
• Thus the problem reduces to one of finding the velocity field incident onto each propeller blade for each source at any radial location.
• This is done by decomposing the incident velocity produced by each ‘source’ into ‘gusts’ of the form
{ }ikxtivk +ωexp
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Tone Sources
• There are several sources of noise produced by an AOR…• Rotor alone tones
– Produced by rotating thickness and steady loading sources – The acoustic source term is calculated directly from the lift and
drag data, which is usually provided by the propeller manufacturer, or could be calculated to a moderate degree of accuracy from simple aerodynamic theory
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Tone Sources
• Viscous wake interaction tones– Produced by the wake from an upstream blade or pylon interacting with
downstream rotor blades
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Tone sources
• Viscous wake interaction tones– Parry gives several expressions for the wake deficit velocity as a
function of upstream rotor drag, chord length and separation distance between the upstream and downstream propellers.
‘Gaussian’ velocity profile( )⎪⎪
⎭
⎪⎪
⎬
⎫
⎪⎪
⎩
⎪⎪
⎨
⎧
⎟⎟⎟
⎠
⎞
⎜⎜⎜
⎝
⎛
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛−∞= 2
2/1
22lnexp2/12/12ln2
bY
XDcC
Uuπ
Yu
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Noise sources
• Bound potential field interaction tones– Produced by the bound potential field (due to thickness and
circulation) on a blade interacting with passing blades on the adjacentrotor
Turbulent wakes generation
Leading edge radiation
Bound potential field
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Bound potential interaction tones
( ){ }∑∞
−∞=−−=
niYXtinvv γωexp
• Note that the upwash decays with streamwise coordinate X, thisindicates that increasing the propeller row separation distance willdrastically reduce this noise source
• This is different from the wake interaction noise source whichdecreases far more slowly with propeller row separation distance
• Parry gives expressions for the upwash onto an adjacent blade produced by the bound potential due to thickness and circulation. A general expression describing the upwash onto the propeller blade is given below
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Tip vortex interaction tones
• Tip vortex produced by large lift gradients close to the propeller tip which produce airflow ‘across’ the blade tip
• Produced by the tip vortex shed from the upstream rotor interacting with downstream rotor blades
Tip-vortex simulation for contra-rotating fans – courtesy DLR
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Noise sources
• Tip vortex interaction tones– Difficult to predict tip vortex parameters, although an empirical model
is available from a NASA study. – This is where CFD simulations (such as those being undertaken at
Cambridge) could give guidance
Tip-vortex simulation for contra-rotating fans – courtesy DLR
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
( )( )⎪
⎭
⎪⎬
⎫
⎪⎩
⎪⎨
⎧
⎪⎪⎭
⎪⎪⎬
⎫
⎪⎪⎩
⎪⎪⎨
⎧
⎟⎟⎠
⎞⎜⎜⎝
⎛
⎟⎟⎠
⎞⎜⎜⎝
⎛Γ−
−
−Γ=Ψχχ
ππ ,/,/0
,/,/0Re22log2/2
2log2/2
4 lrlaHlalrH
lar
rla
alrm
( ) ( ) ( ) ( )∑∞
==
1exp,,0
//
mimmymKmxmmIyxH χχ
{ }kxtikv −ωexp
• Using these expressions the upwash onto a counter-rotating propellerblade can be expressed in the form
• Tip vortex formulation due to Fukumoto (Phys. Fluids 17 pp, 1-17)
Noise sources
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Noise sources
• Stream function (due to tip-vortex) downstream of a five-bladed propeller
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Incidence tones
• Unsteady loading on the blade produced by the propeller propagating at an angle of incidence– This results in the blade undergoing a change in angle of attack as it
rotates, which produces an unsteady load on each blade– The unsteady upwash onto each propeller blade can be expressed as
Side view Front view
Mx
( )⎪⎭
⎪⎬⎫
⎪⎩
⎪⎨⎧ ++Ω= sXrtpcxMv ααα sincossincos0
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Noise sources
• Steady distortion noise– When a spatially varying but steady (in time) flow-field impinges upon
the rotor ‘disc’, as the propeller rotates, the upwash onto the bladevaries with rotor position. This varying upwash produces a periodicloading on the blade and therefore tonal noise
– Sources of steady distortion include,• Flow over wing• Flow over fuselage
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Predicted noise spectrum
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Broadband noise sources
• Rotor self-noise – Produced by the turbulent boundary layer on the surface of the aerofoil
being ‘diffracted’ by the propeller trailing edge• Ingested atmospheric turbulence noise
– Produced by the ingestion and subsequent interaction of atmospheric turbulence by the propeller blades
2.
3.
1.
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Broadband noise sources
• Rotor turbulent wake interaction noise– This is produced when the turbulent wake from the upstream rotor
impinges on the downstream rotor producing broadband noise.
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Installation effects
• Reflection off wing and fuselage
• Propagation effects– Refraction due to atmospheric conditions– Possible ‘hay-stacking’ which may affect the tonal nature of the
spectrum
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
POWERPLANT NOISEAIRFRAME NOISE
Other noise sources
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Whole aircraft noise prediction
• The AOR noise models described above can be implemented into a whole aircraft noise prediction scheme and can be used to calculate the noise from an entire airplane including sources such as airframe and core sources
• The whole aircraft noise prediction software SOPRANO can be used to do this.
• A sample ‘footprint’ for a propeller driven aircraft flying over-head is given below.
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Summary
• This talk has concentrated on the use of analytic methods for predicting AOR noise
• Analytic methods can be used to produce quick noise predictions which makes them ideal for use as a design tool
• Each source must be considered separately • The formulation is difficult, however the analytic models give insight into
dominant noise sources and what parameters affect them• Comparisons with experiments indicate a high level of accuracy
ADVANCED OPEN ROTOR NOISE PREDICTION METHODS
Any questions?